The present invention relates to a control device, including a system and method, for monitoring a generator's phase signals to control the generator's output current and/or electrical current through an electrical system. In particular, the control device monitors two phase signals, generated by the generator phase windings, and responses to a loss of symmetry in the phase signals. The control device achieves this by comparing the two phase signals to one another as opposed to predetermined values. One of the advantages of the present method of relative comparison between two phases is that it eliminates the need to determine other parameters that affect the predetermined values, such as generator speed, electrical load, and direction of rotation. It should be noted that the term symmetry refers to the symmetry between different waveforms associated with the different phases, not for the positive and negative parts of an individual waveform associated with each of the two phases as is the case for traditional determination of AC system health. The loss of symmetry is generally an indication of generator malfunction which may damage the generator itself and/or electrical components in the electrical system. Upon detection of such loss of symmetry, the control device operates to limit or cease the generator output current via the generator output power controller and/or control the magnitude and direction of electrical current through the electrical system via a switch module. Alternatively, the control device may only generate a warning signal in response to the loss of symmetry.
Electrical systems, such as those implemented in modern vehicles or generator sets, include complex electronics and electrical equipment. Such electrical systems are normally comprised of an internal combustion engine and a generator. The engine supplies the generator with mechanical power where it is converted to electrical power. In a vehicle, for instance, the generator generates electrical power for the vehicle electrical system when the vehicle's engine is operating. In a generator set, the engine's mechanical power is converted to electrical power by the generator which is available via power output connectors. Such electrical systems further include energy storage devices such as batteries. The batteries and generator can operate either as a load or a source. Whenever the generator is not operating or can not produce sufficient electrical power, including the engine start process, the batteries provide electrical energy to the electrical system. The generator functions as a source of electrical energy after it attains a certain RPM, at which point electrical power is generated by the generator and delivered to the batteries and other electrical power consuming components within the electrical system.
Ordinarily, the generator includes a voltage regulator that maintains the generator voltage at a regulation voltage. Modern generators include a control device that, in addition to regulating the generator voltage, operates to monitor the generator performance in relation with the vehicle electrical and mechanical system. For instance, in a commonly assigned U.S. Pat. No. 7,466,107 entitled “System and Method for Electric Current and Power Monitoring and Control of a Generator,” hereby incorporated by reference in its entirety, a control device in combination with a generator was disclosed where the control device operated to limit or cease the generator output current in response to an overload detected by measuring a voltage drop across a conductor embedded in the generator. The control device further operated to control the generator output current as a function of battery temperature, battery type, battery voltage, and the ratio between the RPMs of the engine and generator. Also, see Jabaji, U.S. Pat. No. 7,276,804 where a voltage regulator has been disclosed which, in addition to regulating the generator output voltage, operates to discern and respond to regulator, generator, and vehicle electrical system operation and malfunctions; Becker et al., U.S. Pat. No. 6,184,661, where the control device operates to limit the generator output power in order to protect the engine from excessive generator torque; and Jabaji, U.S. Pat. No. 5,907,233, where the control device monitors the AC signal generated by the stator windings and, in the absence of the AC signal, removes the field coil current in order to protect the battery from excessive drain.
In order to provide supplemental monitoring, diagnostics, and control functions, the control device may monitor the signals generated by the phase windings and control either or both the generator output current, and the magnitude and direction of electrical current through the electrical system. It should be noted that the present invention is not limited to sinusoidal, square, quasi-square, or any other form of symmetric waveform. A typical generator comprises stator windings that produce the generator output current via a varying magnetic field. Multi-phase generators have multiple stator windings that are connected via Δ (delta) or Y arrangement, known to skilled artisans. Each phase carries a proportional amount of the total generator output current. For instance in a 3-phase generator, each phase carries approximately ⅓ of the total generator output current, assuming the phase windings are identical.
Generators produce electrical power via their phase windings. In a multi-phase generator, the total electrical power generated by the generator is the sum of the electrical power generated by the individual phase windings. Accordingly, monitoring their performance can be useful in determining the performance of the generator. The signals generated by the phase windings can be compared to ascertain fault conditions associated with the generator. A loss of symmetry in the phase signals most likely is an indication of a malfunctioning generator. As stated above, the term symmetry refers to the symmetry between different waveforms associated with the different phases, not for the positive and negative parts of an individual waveform associated with each of the two phases as is the case for traditional determination of AC system health. Specifically, the loss of symmetry could be due to shorted phase windings and/or one or more faulty rectifying diodes. When such malfunctions occur, it is desirable to control the output current of the generator and/or the magnitude and direction of the electrical current in the electrical system.
In general, a shorted phase winding produces such excessive temperatures that the event can lead to total generator failure. The shorted phase could be due to a short between windings, within winding turns, alternator casing, etc. The rate at which the temperature of the phase windings reaches the point of catastrophic failure depends on the electrical load being delivered by the generator. When the generator is operating at or near full load, these extreme temperatures occur in a relatively short period of time. Such catastrophic temperatures could be delayed or avoided if the generator output current is limited or ceased. Preferably, upon detection of a shorted phase winding, it would be desirable to turn off the generator output current before it undergoes irreversible damage. However, there are many situations in which the electrical system solely depends on the generator output power to provide electrical power to the electrical devices within the electrical system. Under these circumstances, it is desirable to limit the generator output current to avoid the extreme temperatures while delivering enough power to vital components within the electrical system until the generator is repaired. Additionally, a warning or a control signal can be generated to either warn the operator to reduce the electrical load by manually switching off certain electrical components, or to apply the control signal to a switch module to automatically disconnect unnecessary electrical loads.